1. Field of the Invention
The present invention relates to a method of optical resolution of (.+-.)-2-amino-1-butanol and/or (.+-.)-mandelic acid.
2. State of the Art
2-Amino-1-butanol (hereinafter referred to as "AB") is a compound produced only by chemical synthesis. It is used for synthesis of pharmaceutical and cosmetic products, and as a surface active agent, a vulcanization accelerator, a leather treating agent and in textile treating agents (as an emulsifier for polishing agents and detergents). Particularly, (.+-.)-form of AB is essential as an intermediate compound for synthisis of 2,2'-(ethylene diimino)-di-1-butanol, which is a medical compound having a certain therapeutic effect. (U.S. Pat. No. 3,176,040)
To date, with respect to the optical resolution of (.+-.)-AB, there has been known the methods in which
(1) L-tartaric acid is used as the optical resolution agent; Brit. Pat. No. 1,188,185 (1970); J. Am. Chem. Soc. 76 2801 (1954); Chimia 23 399 (1969); and Hung. Pat. No. 157,225 (1970), and,
(2) L-glutamic acid is used as optical resolution agent; Span. Pat. No. 357,033 (1970).
These methods utilize optically active acids in natural occurrence and easily available as the resolution agents. Because the solubility, depositability and hygroscopicity of the salts formed by these optically active acids and (.+-.)-AB are unfavorable for the resolution operation under usual conditions, much difficulty is experienced in practice. Moreover, these methods suffer from low resolution efficiency and low optical purities of the products. Thus, the known methods are not advantageous as the commercial processes.
On the other hand, there has been a demand for the optically active mandelic acid (hereinafter referred to as "MA"), because the optically active forms thereof came to be used as a material for medicines, and because they are useful as optical resolution agents. As to obtaining the optically active forms of MA, it has been proposed to use ephedrine or cinchonine. These resolution agents are, however, not easily available in a large quantity. The resolution procedures are complexed and of low efficiency. Further, it is difficult to obtain pure optically active substances.
Japanese Patent Disclosure No. 24849/1979 discloses a method of optical resolution of (.+-.)MA, which comprises reacting (.+-.)MA with (-)AB in a solvent to form diastereomeric salts, separating the precipitated salt from the mother liquor, and decomposing the diastereomeric salts, one of which is the separated crystal and the other remains in the mother liquor, with an acid and an alkali so as to separately recover the optically active acids and (-)AB
This method uses optically active (-)AB as the resolution agent as noted above, and therefore, the method requires the preceding step of optical resolution of (.+-.)AB. Unless an inexpensive and convenient method of optical resolution of (.+-.)AB is provided, the disclosed method could not mature in a commercially practicable process.